In recent years, hybrid vehicles and the like employ a permanent magnet type synchronous motor, and conventionally there have been proposed a variety of stator cores contemplated to facilitate assembling stators.
For example, Japanese Patent Laying-Open No. 05-095645 describes a stator core including an inner stator core having an outer circumferential surface with a plurality of elements each having a coil wound thereon and an annular outer stator core having an inner circumferential surface with the inner stator core attached thereto.
Furthermore, Japanese Patent Laying-Open No. 2004-328965 discloses a stator including a cylindrical fixing member and a stator core with a core having teeth and press-fitted in the fixing member and thus formed annularly.
A core has one end adapted to have a large circumferential length and the other end adapted to have a small circumferential length, and each core is combined such that the end having the large circumferential length and the end having the small circumferential length are alternately disposed to configure a stator core.
Configuring a stator core is not limited to press fitting divided stator cores into a cylindrical housing to configure the stator core, as described for example in Japanese Patent Laying-Open No. 2004-328965; it is also done by fixing a plurality of annularly arranged divided stator cores by an annular fixing member by shrink fitting or the like.
Any of press fitting and shrink fitting as described above is done generally with each member provided with a tolerance in view of fabrication.
As such, when divided stator cores are annularly fixed to configure a stator core, a divided stator core may project inward in a radial direction of the stator core or be slightly rotated and thus fixed.
Thus the divided stator cores may not have their respective stator teeth with their respective end surfaces, as seen in the radial direction, aligned on the circumference of a single circle and may have a stator tooth projecting radially inward. If a stator core configured as described above has a rotor disposed therein and the rotor is driven, the attraction caused between the rotor and the stator core varies for some position and the rotor may vibrate or contact the stator teeth.
If any of divided stator cores is rotated and thus fixed, the divided stator core and a divided stator core adjacent thereto have a gap therebetween, resulting in a magnetic resistance higher than that between other divided stator cores. This causes variation in distribution of magnetic resistance in the stator core in a circumferential direction and in the fabricated stator core a magnetic flux deviates.